Generally, a wind turbine includes a turbine that has a rotor that includes a rotatable hub assembly having multiple blades. The blades transform wind energy into a mechanical rotational torque that drives one or more generators via the rotor. The generators are sometimes, but not always, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the rotor for the generator to efficiently convert the rotational mechanical energy to electrical energy, which is fed into a utility grid via at least one electrical connection. Gearless direct drive wind turbines also exist. The rotor, generator, gearbox and other components are typically mounted within a housing, or nacelle, that is positioned on top of a base that may be a truss or tubular tower.
In order to supply power to the power grid, wind turbines need to conform to certain requirements. For example, wind turbines may need to offer fault-ride through (e.g. low-voltage ride through) capability, which requires a wind turbine to stay connected to the power grid during one or more grid faults. As used herein, the terms “grid fault,” “fault,” or similar are intended to cover a change in the magnitude of grid voltage for a certain time duration. For example, when a grid fault occurs, voltage in the system can decrease by a significant amount for a short duration (e.g. typically less than 500 milliseconds). In addition, grid faults may occur for a variety of reasons, including but not limited to a phase conductor being connected to ground (i.e. a ground fault), short circuiting between two or more phase conductors, lightning and/or wind storms, and/or a transmission line being connected to the ground by accident.
In the past, during these inadvertent faults, it has been acceptable for a wind turbine to be immediately disconnected whenever the voltage reduction occurs. However, as wind turbines continue to increase in size and penetration of wind turbines on the grid increases, it is desirable for the wind turbines to remain on line and ride through such disturbances. In addition, it is also important for the wind turbines to generate energy after the fault is cleared. Thus, many modern grids utilize auto-reclosing transmission lines that immediately close after a fault is detected so as to subsequently isolate the faulted section for a small time frame (e.g. 1 to 2 seconds). While the initial fault creates a zero or low voltage event, the isolation of the fault (i.e. from closing the transmission line) allows for rapid recovery of the grid voltage. With the auto-reclosing control scheme, however, the faulted line may be reconnected before the fault has cleared, thereby causing one or more subsequent faults. Such control technologies may result in undesirable oscillations in the wind turbine, e.g. in the drivetrain, thereby negatively impacting the lifecycle of the turbine or resulting in a trip of the wind turbine.
Therefore, it is desirable to provide a wind turbine having improved fault-ride through capability that addresses the aforementioned issues. For example, a wind turbine having improved fault-ride through capability that experiences fewer oscillations from one or more grid faults in the power grid would be advantageous.